Voltage regulators that provide AC/DC rectification typically include a full wave voltage rectifier stage, such as, for example, a diode bridge, a main Switch Mode Power Supply (SMPS) stage, and a Power Factor Correction (PFC) stage inserted between the line and the main SMPS. The SMPS provides regulation of an output waveform and the PFC stage draws a sinusoidal current from the line and provides Direct Current (DC) voltage to the main SMPS. Depending on the desired output power, the PFC stage may include a large inductor. However, large inductors are unsuitable for use in systems such as, for example, Liquid Crystal Display (LCD) television power supplies, in which it is desirable to use components having low profiles. To decrease the size of the magnetic components of a PFC stage and thereby lower their profile, manufacturers split the PFC stage into smaller parallel sub-stages that operate out of phase from each other. When the PFC stage is split into two parallel sub-stages they operate 180 degrees out of phase from each other. This configuration is referred to as being an interleaved PFC. Generally, the two PFC stages operate in Critical Conduction Mode (CRM). Because the two PFC stages are out-of-phase from each other, the total input current has the shape of a continuous conduction mode PFC which results in a lower input/output Root Mean Square (RMS) current and easier Electromagnetic Interference (EMI) filtering of the power supply. A drawback with the CRM operating mode is that the switching frequency varies as a function of the line voltage and the power, which precludes the use of a traditional oscillator to achieve the desired phase relationship between the sub-stages. One technique for overcoming this drawback is a master/slave approach where one branch is the master and the other branch is the slave. Here the master branch operates as a CRM single phase PFC. The main challenge of this technique is to maintain the CRM operation, as an unbalance between the PFC stages or a disturbance in the circuit may cause the slave branch to operate either in Continuous Conduction Mode (CCM) or in a discontinuous conduction mode (DCM). Thus, this approach may require some complex and expensive circuitry. Another technique is to operate both branches independently from each other. Here, each phase operates independently in CRM and interacts to set the proper 180° phase shift.
Accordingly, it would be advantageous to have a circuit and method for generating a clock signal for each branch of an interleaved PFC stage. It would be of further advantage for the circuit and method to be cost efficient to implement.